The present invention relates generally to systems and devices used in flexographic, gravure, offset and corrugated board printing as well as in laminating/coating industry. Flexography is a printing process that is used predominantly in the printing of packaging materials. Flexography may be used to print corrugated containers, folding cartons, paper sacks, plastic bags, milk and beverage cartons, disposable cups and containers, labels, adhesive tapes, envelopes, etc. Typically, a substrate is fed into the press from a roll, and is printed upon as the substrate is pulled through a series of print units, each of which prints a single color. The colors of the different print stations are overlaid to create the desired image. Each print unit includes several rollers, such as an ink roller, meter roller, plate cylinder, and impression cylinder. An anilox roller is a type of meter roller that may be an engraved metal or ceramic roller, and that transfers ink from the fountain roller to the printing plate. The characteristics of an anilox roll determine the amount of ink that will be transferred to the plate. Such rolls are typically constructed of a hard metal core that is coated by ceramic, chrome, and other metalls, and whose surface contains millions of very fine dimples, known as cells. The substrate then moves between the plate cylinder with the printing plate and the impression cylinder. The impression cylinder applies pressure to the plate cylinder so the image is transferred from the plate to the substrate.
Over time, the cells of anilox rollers may become fouled with dried ink. The dried ink limits the amount of ink that may be carried by the anilox roller, and reduces the effectiveness of the roll. Therefore, anilox rollers must be cleaned periodically.
Prior art methods of cleaning anilox rollers include using mechanical cleaning, chemical solvents, soda blasting, and ultrasound processes. Each of these methods has certain drawbacks.
Mechanical methods involving brushes or other mechanical abrasives are slow and may damages the surface of the roll. The use of chemical solvents to clean anilox rolls also face a number of disadvantages. In some methods of chemical cleaning, the use of chemical products to remove ink also involves a manual action by means of brushes. While this operation can be performed while the roller is rotating, the mechanical action and chemical cleaner application must be carefully synchronized. Once manual cleaning is over, the roller must be washed immediately to remove the caustic agent and the product wastes. Another method involves off-line cleaning by way of caustic chemicals that dissolve the ink residue in the cells. Such methods typically involve partial immersion of the rollers in a bath of cleaning solution or the chemicals are sprayed on the roller. In both cases, the chemical agent gives rise to a chemical reaction to dissolve the ink deposits. At the end of the cycle, the roller is washed with water to stop the chemical reaction and to remove the cleaning product and the ink wastes. Chemical solvents are, however undesirable due to their environmental impact and potential harm to people. In addition, the costs of removing waste products can be substantial.
Another common method for cleaning anilox rolls involves soda blasting. While cleaning by way of soda is relatively easy to use and causes low environmental impact, there are still shortcomings. For example, soda blasting involves high pressure spraying of soda in water. Spraying the roll evenly is difficult. Also, the soda may cause damage to the material defining the cells, especially with a ceramic surface. Similar to chemical cleaning, the disposal of waste products can also be substantial.
Yet another method involves spraying crystals of solid carbon dioxide (dry ice) onto the cylinders. As with soda blasting, the potential for harm to the anilox roller surface with this method is substantial.
Another system for cleaning anilox rolls involves ultra-sound systems. While such systems are unlikely to cause damage to the rolls and do not suffer from environmental issues, the speed of such systems is somewhat limited, thus leading to greater downtime.
A more recent technology that has been used involves using a laser to clean the anilox roll. A laser beam is moved along a path over the surface of the anilox roll and the laser beam burns off the dried ink. An example of such technology is described in the inventor's Spanish patent 2,390,039, the teachings of which are incorporated herein by reference.
This earlier technology, while proving to be very effective to clean anilox rollers, still faces some shortcomings. For example, in order to cause the laser beam to move along desired patch on the surface of the anilox roll, the laser beam is directed by a reciprocating or oscillating mirror. Because the laser was oscillated by a scanner or mirror in a back and forth pattern across a field, the scanning speed was limited. A further issue with the earlier technology related to the fact that anilox rolls come in different diameters. Because of this, the optimal focal point for the laser may not be easily obtained for a particular roll without adjustment of the roll relative to the laser generator.